The present invention relates to a brushless rotary machine with an AC exciter and a rotary rectifier and, more particularly, to a brushless rotary machine well adaptable for high speed operation.
In recent years, there has been great need for brushless rotary machines because they are maintenance free. Brushless rotary machines have found increasing practical use in a variety of fields for the same reason. FIG. 1 shows a longitudinal sectional view of a structure of a conventional brushless rotary machine. In the figure, a rotating shaft 12 of a rotating electric machine body proper 10 is provided with a rotary rectifier 14 and an AC exciter 16. An AC output generated in the rotor of the exciter 16, with the rotation of the shaft 12, is converted into a DC output by means of the rotary rectifier 14. The DC output is supplied to a field winding 18 of the body proper 10 for exciting the field winding 18.
The rotary rectifier 14 is provided with a cylindrical ring 20 coaxially fitted around the rotating shaft 12, a cooler 24 provided on the inner surface of the cylindrical ring 20 through an insulating member 22, and a rectifier element 26 fixed to the cooler 24. The rectifier element 26 is cooled as the result of heat exchange of the rectifier element 26 with cooling air when fins 28 provided on the side wall of the cooler 24 rotates with rotation of the shaft 12 to exchange heat of the fins 28 with cooling air.
As shown in FIG. 2 the rotary rectifier 14 is provided with the rectifier element 26 fixed to the cylindrical ring 20 through the insulating member 22 and the cooler 24, the ring 20 being fitted to the rotating shaft 12. Therefore, the rectifier element 26 must be mounted at the outer periphery of a fitting ring 20a of the cylindrical ring 20 for fitting the cylindrical ring 20 to the rotating shaft 12, isolated from the fitting ring 20a. The mounting position of the rectifier element 26 depends on the diameter of the rotating shaft 12 and the fitting portion 20a. Accordingly, it must be located at the far radially outer side in the rotary machine. With this structure, the centrifugal force developed when the rotating shaft 12 rotates at the speed of 3,600 rpm or more is very high. The centrifugal force applied to the rectifier elements 26 exceeds the limit of the withstanding strength. The result is insufficient and unstable rectification. Thus, it becomes impossible to operate the brushless rotary machine at ultra high speed.
The mounting position of the cooler 24 for cooling the rectifier element 26 is at the radially outer side location in the machine. When it rotates at high speed, friction heat with air becomes high since it contacts the air at a high speed. This lessens the cooling effect. Therefore, for keeping the temperature generated from the rectifier element 26 below a limit, the current capacity of the rectifier element 26 must be reduced.
As described above, the conventional rotary rectifier has problems in mechanical strength and cooling function arising from the mounting position of the rectifier elements. The problems are very serious since the rectifier element is a semiconductor device which is mechanically fragile and sensitive to ambient temperature.